Lomas de Zamora, Argentina
Facultad de Ciencias Agrarias Cátedra de Fisiología Vegetal (UNLZ)

Llavallol, Argentina
Instituto Fitotécnico de Santa Catalina (UNLP)

Germination of Andean Patagonian maize (Zea mays ssp. mays) inbreds selected for cold tolerance

--Huarte, HR, Jatimliansky, JR, Molina, MC

Maize is one of the most economically important crops in the world. In both hemispheres, the sowing region is located between 47 °C and 30 °C (temperate and sub-tropical areas). This distribution is due to the tropical origin of the species, which makes it sensitive to low temperatures. Cold susceptibility is one of the greatest constraints that limits maize's spread to new sowing areas for both commercial or subsistence purposes. Brandolini et al. (Brandolini, A., et al., Euphytica 111:33–41, 2000) pointed out that the ability of a determined genotype to germinate, emerge and grow vigorously under low temperatures, constitutes a remarkable characteristic the impact of which extends beyond the cold regions. Effectively, the use of cold tolerant maize genotypes in the most suitable regions for cultivation offers some agronomic advantages such as an earlier sowing date, and its introduction into regions currently considered marginal because of their low temperatures makes maize cultivation more successful.

In the case of maize, 10 °C is commonly accepted as a base temperature (Tb) and 25 °C as an optimum temperature for growth (To). Nevertheless, Rench (1973) determined 7.2 °C to be the base temperature for growing. Several studies reported the existence of genetic variation both for germination and growth under low temperature conditions (Eagles, H and Brooking, IR, Euphytica 30:755–763, 1981). There is also evidence that genetic cold stress tolerance could be found in exotic germplasm such as those obtained from the Andean region (Brooking, IR Maydica 35:35–40, 1990). Due to the facts mentioned above, the objectives of this study were: I) Identifying within the materials evaluated, those able to germinate under low temperatures. II) Elucidating whether the eventual ability to germinate under low temperatures is due to a lower Tb for germination.

Seeds of 12 different genotypes were used. The materials were multiplied in the experimental field of the Instituto Fitotécnico de Santa Catalina (IFSC) (latitude 34° 48′ S, longitude 58° 31′ W) Argentina, during the growing season of 2000/01. Genotypes labelled SC from 1 to 7 are short cycle materials belonging to populations from NW Argentina Patagonian and the X^th Chilean region. SC 9 is a mid cycle genotype obtained at the IFSC. Two French inbreds (L 10 and L 11) and an American one (B 73) were used as testers.

Five replicates of 20 seeds each were incubated at constant temperatures from 10 °C (± 0.5) up to 35 °C (± 0.5 °C) with intervals of 5 °C. Testing lasted 7 days when incubation temperatures were 20 °C or higher, and 14 and 28 days when germination occurred at 15 °C or 10 °C, respectively. Seeds were placed in 9 cm diameter Petri dishes on two discs of filter paper and hydrated with 6 ml of distilled water (equilibrated at the corresponding temperature). Seeds with a clearly visible radicle protrusion were considered germinated.

The following variables were considered:

1. Final germination percentages at 10 and 25 °C
2. Germination index proposed by Smith & Millet (Smith, PE and Millet, AH, Proc. Am. Soc. Hort. Sci. 84:480–484, 1964) was calculated as follows.[∑(number of seeds germinated on a given day)(number of days after planting)]/ total number of seeds germinated at the end of the trial
3. The base temperature for germination (50 %) was calculated for each of the materials included in this study.

Data obtained in I and II were analyzed by ANOVA and Tukey’s test (α=0.05).

Significant differences (P<0.05) among the genotypes evaluated were found in germination under stress treatment as well as the control test (25 °C). Under stress treatment, Andean inbreds showed germination percentages higher than the testers (P<0.05)(Table 1). The germination index (GI) obtained for SC 1 and SC 3 under stress treatment also exceeded the testers, denoting a higher germination rate (P<0.05)(Table 1).

Stress: Germination test at 10 °C for 28 days.
Control: Germination test at 25 °C for 7 days
Different letters within the same column designate significant differences (p<0.05) according to Tukey´s test

The germination temperature base for all Andean inbreds was lower than that calculated for the testers and other genotypes of different origin (SC 9 and SC 12)(Table 2). In this sense the values calculated for this parameter in some Andean materials (SC 7, SC 4 and SC 1) are substantially lower than those previously reported for maize (e.g. = 7.2 or 10 °C)

Germination percentages at 10 °C of the Andean-Patagonian inbreds were greater than those from the selected testers employed (Table 1). In addition, one of these inbreds, SC 1, also showed the highest germination index.

SC 1, SC 4 and SC 6 temperature base for germination was 3 °C lower than for B73 (Table 2). This fact is in accordance with the higher GI observed in some Andean inbreds exposed to stress treatment. Data presented in this communication show that some Andean-Patagonian inbreds are promising basic materials for developing new cold tolerant hybrids.